1. Field of the Invention
The present invention relates to a radiator, and more specifically, to a radiator having a fan in variable rotation speed.
2. Description of the Prior Art
Common radiators include cooling fins and fans. Most of the cooling fins are composed of aluminum alloy while a small number uses other materials, but all of them have almost the same heat conductivity. Besides composing materials, the performance of a cooling fin depends also on its surface area. A cooling fin conducts heat to its surface so that the air can bring the heat away, thus the larger the surface area is, the better the performance of the cooling fin is. However, the cooling fin does not work well if the air flow is insufficient even if it has a large surface area, thus for a better performance, a fan promoting air flow is necessary. Generally, the higher the rotation speed, the better the performance of the fan. That is because the fan accelerates the air flow in high rotation speed so that the air can bring more heat away. The rotation speed of the fan can be known by its power consumption. A fan consuming more power rotates faster.
Please refer to FIG. 1 showing a conventional radiator 10. The radiator 10 includes a thermal sensor 12, a microcontroller 14, a driver circuit 16 and a fan 18. The interconnection between devices of the radiator 10 is shown in FIG. 10. Generally the radiator 10 is installed in a system, the thermal sensor 12 is for sensing the temperature of the system, the microcontroller 14 compares the temperature sensed by the thermal sensor 12 with a predetermined temperature, and the driver circuit 16 turns on the fan when the temperature sensed by the thermal sensor 12 exceeds the predetermined temperature. The driver circuit 16 can output different voltages according to the requirements by the microcontroller 14 to control the rotation speed of the fan 18, and the fan 18 has a signal line connected to the driver circuit 16 for outputting a speed signal of the fan 18. Whenever the thermal sensor 12 senses a temperature raising, the microcontroller 14 requires the driver circuit 16 to speed up the fan 18, so that the driver circuit 16 raises up the output voltage to the fan 18, and when the speed of the fan 18 is raised up, the signal line transmits the speed signal back to the driver circuit 16. And if the thermal sensor 12 senses a decrease in temperature, the speed of the fan 18 should be lowered down to conserve power, so that the microcontroller 14 requires the driver circuit 16 to lower down the output voltage to the fan 18, and the driver circuit 16 knows the speed of the fan 18 by the signal line.
As mentioned above, the conventional radiator capable of controlling the rotation speed of the fan 18 uses the thermal sensor 12 to sense the environmental temperature, the microcontroller 14 compares the temperature sensed by the thermal sensor 12 with the predetermined temperature and requires the driver circuit 16 to control the speed of the fan, and the driver circuit 16 to compare the feedback speed signal of the fan 18 with the speed signal required by the microcontroller 14 in order to control the output voltage to the fan 18 to change its rotation speed, so that the speed of the fan 18 can be adjusted according to the environmental temperature. However, the radiator 10 requires the thermal sensor 12, the microcontroller 14 and the driver circuit 16 which raise the cost. In addition, the temperature comparison by the microcontroller 14 and the rotation speed comparison by the driver circuit 16 also lower down the sensibility of the radiator 10.